The desire to apply a layer of material onto a target surface exists in a lot of different technological areas. There are various reasons for applying materials to surfaces, with the most common being the desire to fulfil aesthetic demands such as the desire to apply certain, often multi-coloured, graphical patterns onto the surface or on certain areas of the surface or to protect the surface against environmental influence. An application of a desired pattern according to the present invention can for example also be used in areas where in prior art decals were used for embellishing or decorating a surface with a desired pattern or to apply desired markings on the surface.
The technical areas wherein such painting, spattering, inking, dyeing or coating is desired, range for example from construction work, advertising, amusement, markings on sport grounds, road marking, camouflaging, car manufacturing, machinery building, indoor and outdoor wall claddings, applying advertisements to large trucks, semi-trailers, buses, aircrafts, vessels, etc. Also, a repair of already—at least partially—painted or decorated surfaces which became worn out, damaged, sabotaged, partly replaced, etc. is often required. In such repair or replacement work, it is desired to achieve a high degree of colour and pattern matching for a smooth and optically uniform transition from the old to the new application.
Painting a pre-defined pattern such as a logo or an image, which is digitally available as a picture, CAD file, etc. and which should be applied to a surface, can be quite demanding. Using a brush or airbrush requires a skilled craftsman, who needs experience and knowledge in the guidance and reliable handling of the tool, as well as knowledge of paint viscosity, drying conditions and various other parameters during labour. Another, industrially often used solution is to mask the undesired areas of the target surface by adhesive tapes and/or adhesive foils, which are removed after the application has finished. Another approach is to directly apply decorated adhesive foils or decals to the target, as substrates already carrying or shaped to the desired pattern. In any case, an additional layer of transparent over-coating can be required to protect the artwork and/or to achieve a smoother surface.
A common principle used to apply material onto a surface is to expel or eject the material—such as paint—from a nozzle means onto a target surface. The so called inkjet technology was first disclosed in the British patent Nr. 2,147 by Lord Kelvin and from thereon continuously evolved to the present continuous (CIJ) and Drop-on-demand (DOD) technology as e.g. used in contemporary ink-jet printers, where the DOD technology is often embodied by thermal DOD or piezoelectric DOD. New ink-jet technology, which is expelling droplets of spattering materials out of a nozzle in a well defined manner (comparable to the systems used in the abovementioned contemporary ink-jet printers for home or office use) is available to paint with narrow spot sizes of less than one centimeter even from 10 cm distance. Such low divergence expelling techniques allow an application of a desired pattern without masking the desired target area and a real-time colour mixing or colour changing, colour fading from one colour to another or the like. Ink-jet material deposition is also an emerging manufacturing technique in which ink-jet technology is used to deposit materials on substrates in order to build up 3D objects.
As example for surface applications, the document FR 2 850 322 discloses a device for printing an image on a large surface that may be held and moved manually. The device, which is able to determine position and direction on a surface, uses the knowledge of its current position to determine which colour needs to be applied onto the surface. This determination is accomplished by matching the determined coordinates and an image stored in a memory of the device. The stored image may then be superimposed to the surface to be painted.
JP 2006-320825 shows a self-regulating painting vehicle for a uniform paint coating an aircraft. It includes arm control means to control operation and movement of an arm with an actuator head. A painting process with respect to a surface to be uniformly coated is performed based on the information of the coating area stored in a memory means and the attitude and position information of said arm. The position of the vehicle and the head are determined using a GPS and a rangefinder measures the distance between the head and the aircraft surface.
WO 03 066 239 discloses an application of paint on architecture in accordance to a digital image by a movable applicator. The applicator has an array of nozzles for expelling paint fixed to its body which are moved over the surface, in particular by hand. Paint is only applied if a real time determined position of the applicator is within an acceptance threshold. US 2006/221,403 shows a similar device for a handheld application of a desired pattern.
US 2009/0022879 relates to a method for applying paints or varnishes to large surfaces by means of a displaceable, paint applying device which is controlled in a position-dependent manner. Said device comprises a displaceable part of a real time position measuring system which uses reference marks fixed at known positions on the surface.
US 2008/152,807, US 2011/199,431, U.S. Pat. No. 7,350,890 and U.S. Pat. No. 7,922,272 are referring to methods and devices for applying an accurately positioned graphic image on a large contoured surface, such as the body of an aircraft. The apparatus used therein comprise a rail guidance system to be mounted on a portion of the surface on which the graphic image is to be applied. The graphic image application system is controlled by software to operate a positioning system and a graphic image application system. In EP 1 987 889 and US 2006/044376 a paint applicator is automatically moved within a Cartesian coordinate frame structure.
The mounting of such guide rails can be quite challenging. Their position and/or orientation is influencing the result of the application, e.g. in its position and/or orientation on the target surface and also the alignments of multiple tiles relative to each other. Also, the mounting of the guides is quite time consuming and as the target objects do not provide referenced fixation means for such guides, suction cups, lashing straps or belts around the target have to be used to attach the guides, which are difficult to apply with high positional accuracy.
In U.S. Pat. No. 6,096,132 a distance sensor is used to control a three dimensionally movable nozzle to achieve a constant application distance. U.S. Pat. No. 6,360,656 determines an inclination of the target surface and adjusts the expelling accordingly. In US 2010/304,009 a sensor at the applicator determines a three dimensional shape of the target surface and therewith controls and coordinates the 3D movement and expelling of the applicator to produce a desired a picture-motif on the target.
EP 2 433 716 concerns a handheld, surface spattering device with a nozzle and a nozzle control mechanism to control characteristics of the expelling of the nozzle. A spatial referencing unit references the spattering device relative to the target surface and a computation means controls the expelling according to the spatial referencing to achieve a desired spattering.
As it is not feasible to apply large desired patterns to a target at once, in a single application step, the desired pattern has to be split into sections or tiles, which are subsequently applied. Therein, the alignment of the borders of the individual tiles of such subsequent applications, have to be accurately aligned, in particular as human observers are very sensitive for misalignments. Nevertheless, by an application which is only based on a direct alignment of the tiles against their direct neighbour, the whole of the large pattern tends to be distorted or misaligned on the target surface. Only slight inaccuracies of the tiles and their position and/or orientation will sum up and end not only in an inaccurate position and orientation of the large pattern as a whole but also in geometrical conflicts of the tiles, like gaps, overlappings, etc.